The temperature-sensitive mutation vir ts(virilizer) identifies a new gene involved in sex determination of Drosophila.

When XX animals homozygous for the temperature-sensitive mutation vir tsof virilizer (2-103.9) are raised at the restrictive temperature of 29° C, they are transformed into sterile intersexes with a morphology comparable to XX flies mutant at the sex-determining gene doublesex (dsx). The gonads of the vir tsintersexes are ovaries in which the germ cells undergo abortive oogenesis. At the permissive temperature of 25° C or below, XX vir tsanimals develop into marginally fertile females. The temperature-sensitive period of vir tsis within the third larval instar. XY males are not affected by the mutation. Animals that are homozygous for vir tsand either transformer (tra) or tra2 develop as pseudomales; on the other hand, constitutive expression of a female-specific tra product rescues XX animals from the effect of vir ts, but these females are sterile. The data show that tra and tra2 are epistatic to vir. Animals with only one wildtype copy of either tra or tra2 and mutant for vir tsare already transformed into intersexes at 25° C. Conversely, the presence of three copies of the tra + gene largely prevents the effect of vir tsat 29° C; such flies are practically female, but sterile. Animals homozygous for vir tsand heterozygous for dsx D/+, raised at 29° C, are transformed into severely masculinized intersexes or almost pseudomales. The observations suggest that vir acts above and via tra and tra2 to achieve proper female-specific expression of the dsx gene in XX zygotes.